Focal adhesion kinase modulates activation of NF-κB by flow in endothelial cells

Abstract

genesis involves activation of NF-B in endothelial cells by fluid shear stress. Because this pathway involves integrins, we investigated the involvement of focal adhesion kinase (FAK). We found that FAK was not required for flow-stimulated translocation of the p65 NF-B subunit to the nucleus but was essential for phosphorylation of p65 on serine 536 and induction of ICAM-1, an NF-B-dependent gene. NF-B activation by TNF-␣ or hydrogen peroxide was FAK independent. Events upstream of NF-B, including integrin activation, Rac activation, reactive oxygen production, and degradation of IB, were FAK independent. FAK therefore regulates NF-B phosphorylation and transcriptional activity in response to flow by a novel mechanism.atherosclerosis; fluid shear stress; integrin signaling; mechanotransduction CURRENT MODELS FOR ATHEROSCLEROSIS suggest that local endothelial dysfunction results in monocyte recruitment and lipid deposition in the vessel intima (29). In addition to systemic risk factors, fluid shear stress from flowing blood plays a crucial role. Atherosclerotic lesions develop preferentially in regions of oscillatory or disturbed flow that have lower mean shear stress, multidirectionality, and flow separation (33).The proinflammatory transcription factor NF-B is thought to be a key determinant of atherogenesis (8). NF-B is activated in atheroprone regions in vivo concomitant with expression of its target genes including ICAM-1, VCAM-1 (20), monocyte chemoattractant protein 1, tissue factor, and PDGF (8). NF-B is a dimer, usually consisting of a p65 and a p50 subunit, though other combinations also exist. Inactive NF-B is sequestered in the cytoplasm by IB proteins (8,20). The IB kinase (IKK) complex phosphorylates IB, leading to its ubiquitination and proteosomal degradation. Free NF-B dimer then translocates into the nucleus and binds to B enhancer sites. Phosphorylation, acetylation, and sumoylation regulates the subsequent recruitment of cofactors and other members of the transcriptional machinery required to drive target gene expression.Integrins have been implicated in activation of NF-B and several other proinflammatory pathways in response to flow (19). Shear stress induces conversion of integrins to a high-affinity state (i.e., integrin activation), which is followed by binding of these high-affinity integrins to the extracellular matrix beneath the cells to form new integrinmatrix contacts (53). The newly ligated integrins trigger downstream signals, including RhoA, Rac, and Cdc42 activation (53-55). These GTPases mediate cell alignment, sterol regulatory element-binding protein (SREBP) cleavage (30), and . Consistent with this model, flow-induced activation of NF-B is integrin and matrix dependent, occurring in cells on fibronectin (FN) or fibrinogen but not on collagen or laminin (38).Focal adhesion kinase (FAK), a nonreceptor tyrosine kinase involved in integrin signaling (43,46), is present in endothelial cells and has been implicated in responses of endothelial cells to fluid shear stress. Complete ...

αvβ3 Integrins Mediate Flow-Induced NF-κB Activation, Proinflammatory Gene Expression, and Early Atherogenic Inflammation

“…Inhibiting avb3 similarly blunted shear stressinduced activation of FAK and PAK, pathways known to mediate integrin-dependent NF-kB activation by shear. 8,28 The requirement for avb3 is consistent between the responses to early onset of flow and those seen with chronic oscillatory flow, and avb3 is not required for tumor necrosis factor-aeinduced proinflammatory gene expression, suggesting that avb3 inhibition does not regulate endothelial cell activation in response to all proinflammatory stimuli. We further show that inhibiting av integrins, either with S247 or in the iEC-av KO mice, significantly blunts inflammation in the partial carotid ligation model of oscillatory flow-induced vascular remodeling in vivo, whereas inhibiting a5 did not.…”

“…Inhibiting avb3 (S247, siRNA) blunted shear stress-induced NF-kB activation and activation of FAK and PAK, pathways previously shown to mediate shear-induced NF-kB activation. 8,28 However, shear-induced activation of ERK1/2, AKT, and eNOS (Ser1177 phosphorylation, Thr495 dephosphorylation) remained intact, consistent with integrins mediating only a subset of shear-induced signaling responses. Inhibiting av prevented shear stress-induced eNOS phosphorylation on Ser633; however, its functional significance remains unclear.…”

Sphingosine kinase 1 promotes tumor progression and confers malignancy phenotypes of colon cancer by regulating the focal adhesion kinase pathway and adhesion molecules

“…In endothelial cells FAK was essential for induction of ICAM-1 and sVCAM-1-induced cell migration and was almost completely blocked by adenovirus containing FAK-related non-kinase (33). In human colon cancer, gastrin-releasing peptide was found to induce ICAM-1 via FAK and promoted tumor cell motility and attachment to the extracellular matrix (34).…”

Mechanical Regulation and Maintenance of Organismal Homeostasis - Scientific Basis for Health Promotion by Physical Motility and Exercise

“…Furthermore, shear stress reportedly activates straining-related signaling molecules such as NF-κB and MAP kinases 11) , as well as relaxation-related ones including eNOS 12) . Therefore, shear stress appears to be a mixture or combination of straining and relaxing mechanical stress.…”